X0609 4 2026-08-03 0001776111 MBX Biosciences, Inc. MBX 0001533451 Hoerter Steven L. false C/O MBX BIOSCIENCES INC. 11711 N. MERIDIAN STREET, SUITE 300 CARMEL IN 46032 true true false false President and CEO false Common Stock 2026-08-03 4 A false 71000 0 A 82938 D Common Stock 20000 I Trust Stock option (right to buy) 64.41 2026-08-03 4 A false 331000 0 A 2036-08-03 Common Stock 331000 331000 D Represents the grant of restricted stock units ("RSUs"). 25% of the shares subject to the RSU grant will vest annually over four years, on each July 13, 2027, 2028, 2029 and 2030, subject to continued service on each such vesting date. Shares held by the Steven L Hoerter Revocable Trust dated November 2, 2018, of which the Reporting Person serves as trustee. The Reporting Person disclaims beneficial ownership except to the extent of any pecuniary interest therein, and this report shall not be deemed an admission that such shares are beneficially owned by him for Section 16 or any other purpose. The options will vest and become exercisable with 25% of the shares subject to the award vesting on July 13, 2027 and the remainder vesting in 36 equal monthly installments thereafter, subject to continued service on each such vesting date. Exhibit 24 - Power of Attorney /s/ John W. Smither, Attorney-in-Fact 2026-08-04